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Statistics

Performance

Note: Refer to Do's and Don'ts section of this catalogue for design advice.

Problem

Possible Cause

Recommended Action

Low air flow

Faulty instruments.

Ensure instruments are accurate and calibrated where necessary.

The wrong size fan has been installed.

Check the fan specifications are correct for the particular system.

The fan is running backwards.

Check rotation of the impeller. If the rotation is wrong refer to the 'Electrical' section above.

Pitch-angle of an axial fan may be wrong.

Check the pitch-angle against the schedule, if wrong contact the supplier. Site adjustment may be practical.

Fan speed is too slow.

Check the motor speed and, if belt-driven, the pulley ratios. If wrong change to suit.

To ductwork is undersized.

Check the ductwork and grilles are the correct size. If smaller than design this will increase the system resistance.

If a centrifugal fan check the cut-off position.

Contact the supplier.

Bad installation.

Check the entry and discharge conditions to the fan are of a good design. If the fan is mounted close to bends on the intake or discharge this will impact on the fans' performance. Check there are no duct obstructions on the intake or discharge of the fan. Internal duct lining may have come loose, check and repair.

The ductwork is undersized.

Check the ductwork and grilles are the correct size. If smaller than design this will increase the system resistance.

Fan speed is too low.

Check the motor speed and, if belt-driven, the pulley ratios. If wrong change to suit.

High air flow

Faulty instruments

Ensure instruments are accurate and calibrated where necessary.

The wrong size fan has been installed.

Check the fan specifications are correct for the particular system. If an axial fan check the pitch angle and, if wrong, adjust.

The ductwork is oversized.

Check the ductwork and grilles are the correct size. If larger than design this will decrease the system resistance.

Fan speed is too high.

Check the motor speed and, if belt-driven, the pulley ratios. If wrong change to suit.

System resistance is greater than estimated.

The ducting and/or the grilles, coils etc. may be smaller than design, which will increase the system resistance.

Check that the ductwork and system components are the correct size. Check that all dampers are open, Check that all registers and grilles are open. Check the ducting is clear of rubbish. Check flexible connectors are installed correctly. Check if filters are dirty, clean or replace as necessary. Check if coils are dirty and clean them if necessary. Check duct take-offs and general duct fittings are correctly installed and of good design.

System resistance is lower than estimated.

If the duct system and associated components are larger than design this will reduce the system resistance.

Check the ductwork and associated components are the correct size. Check for leaks around flexible connections.

There may be leakage from the ductwork.

Check the ductwork for leakage and rectify as necessary.

Leakage around the bas of Roof Ventilators.

Ensure there is a proper seal between the unit base and the up-stand. If there is no seal then install one.